linux-kernel - [PATCH] block: Eliminate usage of uninitialized

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Message-ID: <20200615035843.3334350-1-yanaijie@huawei.com>
Date:   Mon, 15 Jun 2020 11:58:43 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     <axboe@...nel.dk>, <bvanassche@....org>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel-hardening@...ts.openwall.com>
CC:     Jason Yan <yanaijie@...wei.com>, Kees Cook <keescook@...omium.org>,
        "Ming Lei" <ming.lei@...hat.com>
Subject: [PATCH] block: Eliminate usage of uninitialized_var() macro

This is an effort to eliminate the uninitialized_var() macro[1].

The use of this macro is the wrong solution because it forces off ANY
analysis by the compiler for a given variable. It even masks "unused
variable" warnings.

Quoted from Linus[2]:

"It's a horrible thing to use, in that it adds extra cruft to the
source code, and then shuts up a compiler warning (even the _reliable_
warnings from gcc)."

The gcc option "-Wmaybe-uninitialized" has been disabled and this change
will not produce any warnnings even with "make W=1".

[1] https://github.com/KSPP/linux/issues/81
[2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Cc: Kees Cook <keescook@...omium.org>
Cc: Ming Lei <ming.lei@...hat.com>
Signed-off-by: Jason Yan <yanaijie@...wei.com>
---
 block/blk-merge.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index f0b0bae075a0..006402edef6b 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -473,7 +473,7 @@ static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
 			     struct scatterlist *sglist,
 			     struct scatterlist **sg)
 {
-	struct bio_vec uninitialized_var(bvec), bvprv = { NULL };
+	struct bio_vec bvec, bvprv = { NULL };
 	struct bvec_iter iter;
 	int nsegs = 0;
 	bool new_bio = false;
-- 
2.25.4